Friday, May 8, 2009

1. E L E C T R O S T A T I C S .3M ANSWERS,

1. E L E C T R O S T A T I C S .3M ANSWERS,

1. DEFINE ELECTRIC LINES OF FORCE.The concept of field lines was introduced by Michael Faraday asan aid in visualizing electric and magnetic fields.Electric line of force is an imaginary straight or curved path alongwhich a unit positive charge tends to move in an electric field.2. STATE THE PROPERTIES OF ELECTRIC LINES OF FORCE.(i) Lines of force start from positive charge and terminate at negativecharge.(ii) Lines of force never intersect.(iii) The tangent to a line of force at any point gives the direction ofthe electric field (E) at that point.(iv) The number of lines per unit area, through a plane at right anglesto the lines, is proportional to the magnitude of E. This meansthat, where the lines of force are close together, E is large andwhere they are far apart, E is small.(v) Each unit positive charge gives rise to 1 εo lines of force in freespace. Hence number of lines of force originating from a pointcharge q is N =q ε in free space.3. DEFINE ELECTRIC DIPOLE.GIVE EXAMPLES.Two equal and opposite charges separated by a very small distanceconstitute an electric dipole. Water, ammonia, carbon−dioxide andchloroform molecules are some examples of permanent electric dipoles4. DEFINE DIPOLE MOMENT.WRITE EXPRESSION,UNIT.The magnitude of the dipole moment is given by the product of the magnitude of the one of the charges and the distance betweenthem. Electric dipole moment, p = q2d or 2qd. It is a vector quantityand acts from –q to +q. The unit of dipole moment is C m. 5. DEFINE TORQUE EXPERIENCED BY ELECTRIC DIPOLE?The magnitude of torque is,τ = One of the forces x perpendicular distance between the forces = F x 2d sin θ = qE x 2d sin θ = pE sin θ (q × 2d = P)Note : If the dipole is placed in a non−uniform electric field at anangle θ, in addition to a torque, it also experiences a force.